Early genetic amniocentesis--4 years' experience

Early amniocentesis

Although amniocentesis was first reported in 1882, the technique was not in widespread clinical practice until the 1970's. The reason for this slow uptake was that there were few indications for performing the procedure until fetal karyotyping from amniotic fluid cells became possible in 1966. Currently fetal karyotyping is the commonest indication for the technique and amniocentesis has become the mainstay of antenatal diagnosis.

First trimester prenatal diagnosis: amniocentesis

Twenty years after midtrimester genetic amniocentesis was first used, first trimester invasive prenatal procedures were introduced. Chorionic villous sampling presents some disadvantages that entitled many centers to look into an alternative for first trimester diagnosis. Early amniocentesis (EA) can be performed effectively, as shown over the years in many observational studies and partially randomized and randomized trials. Recently, a multicenter randomized trial (Canadian Early and Midtrimester Amniocentesis Trial) reported a higher total pregnancy loss, a significant increased incidence of musculoskeletal foot deformities, a significant increased culture failure rate, and an increased postamniocentesis rate of leakage in the EA group compared with midtrimester amniocentesis. These results concerning EA procedures from 11w(+0) to 12w(+6) should be included in any pre-EA counseling. However, further trials have started to evaluate EA procedures between 13w(+0) to 14w(+6).

Cytogenetic aspects of the Canadian early and mid-trimester amniotic fluid trial (CEMAT)

Cytogenetic results from a large multicentre randomized controlled study of 2108 amniotic fluids obtained at 11+0-12+6 weeks (EA) and 1999 fluids at 15+0-16+6 weeks (MA) were compared. There was no statistically significant difference in the rate of chromosome abnormalities (EA =1.9 per cent; MA=1.7 per cent) or level III mosaicism (EA=0.2 per cent; MA= 0.2 per cent) between the groups. Level I and Level II mosaicism occurred more frequently in MA. Maternal cell contamination was not significantly different between the groups, but maternal cells only were analysed from one bloody EA fluid. The number of repeat amniocenteses because of cytogenetic problems was 2.2 per cent in the EA group compared with only 0.3 per cent in the MA group. On average, culture of EA fluids required one day more than MA fluids. Although both culture success (97.7 per cent) and accuracy (99.8 per cent) were high for patients randomized to the EA group, routine amniocentesis prior to 13 weeks' gestation is not recommended for clinical reasons including an increased risk of fetal loss and talipes equinovarus.

Early and midtrimester genetic amniocenteses. Safety and outcomes

Prenatal diagnosis, the in utero determination of fetal disease, has become an important aspect of genetic counseling. The advances in technology coupled with developments in the field of molecular biology and genetics have made possible the detection of an increasing number of diseases in utero. Although not without some risk, midtrimester amniocentesis has been, and will continue to be, an important technique in this regard.

Early amniocentesis at 10-12 weeks' gestation

In this study we report the results of 181 ultrasound-guided genetic amniocenteses performed at 10-12 weeks of gestation and describe the indication, technical problems, amniotic fluid volume, culture success and timing, abortion and fetal loss rate, and perinatal results. Amniotic fluid was obtained in 98.4 per cent of the cases; at the first attempt, in 167 out of 181. The culture success rate was 94.5 per cent, and the fetal loss rate within 2 weeks was 0.5 per cent (one case with a sonographic abnormality). The total fetal loss rate during pregnancy was 1.6 per cent. A comparison of our data and those of other published series shows no significant differences, either with respect to this period of gestation (10-12 weeks) or with respect to the traditionally called early amniocentesis' (12-14 weeks) or conventional amniocentesis (15 weeks or more). The mean culture time was just a few days longer in some of the series, and in some cases, there was also a lower success rate after culture, particularly when amniocentesis was carried out at 10 weeks or less. We conclude that amniocentesis performed at 10-12 weeks is feasible, safe, and easy to perform, and provides a real benefit to the pregnant woman.

Early amniocentesis: a clinical review

Early amniocentesis at less than 14 weeks gestation is becoming more common in prenatal diagnosis populations. Randomized studies are minimal and have not had the power to determine the accuracy and safety of the procedure compared to chorionic villus sampling or mid-trimester amniocentesis. Procedures at 11+0-12+6 weeks should be considered experimental. This clinical review considers the ethics, embryology, and clinical experience (cytogenetics, AFP, AChE, procedure and cytogenetic failures, spontaneous and therapeutic pregnancy losses, congenital anomalies) of early amniocentesis.

Screening for Down's syndrome

Down's syndrome (DS) is the commonest cause of severe mental retardation in children. It is the result of trisomy of chromosome 21 which is usually a random event though it is commoner in older mothers. DS can be diagnosed by chorionic villus sampling (CVS) and amniocentesis followed by karyotyping. Because of the risks associated with these invasive procedures, they can only be offered to a high-risk group. At one time the sole basis for identifying this increased risk was maternal age, but within the past ten years a series of biochemical and ultrasound abnormalities have been shown in DS pregnancies. The biochemical abnormalities include changes in the levels of most fetal and placental products in the maternal circulation. The best-known of these changes are the reduced levels of alphafetoprotein (AFP) and oestriol (E3) and increased levels of human chorionic gonadotrophin (hCG). The mechanism underlying these biochemical phenomena is unknown. Screening programmes involving the measurement of hCG and AFP, with or without additional parameters such as E3, at 15-18 weeks of pregnancy can typically identify 60% or more of cases of DS with a screen-positive rate of 5%. The combined risk derived from the various biochemical parameters, together with maternal age, is calculated by one of a number of computer programmes which have been developed for this purpose. There has been considerable discussion as to the exact biochemical tests which should be used for DS screening. This had led to controversy as to whether measurement of E3 has a place, and whether or not measurement of the free beta-subunit of hCG should replace measurement of the intact molecule. A notable recent development is the suggestion that measurement of the urinary beta-core of the hCG could be a highly discriminatory marker. A number of factors can affect the results of biochemical screening for DS. These include maternal weight, gestational age, ethnic origin, smoking, and diabetes. In addition, abnormal levels of the biochemical products may be found in other chromosome abnormalities.

Early amniocentesis--a cytogenetic evaluation of over 1500 cases

We report our cytogenetic experience of 1554 early amniocenteses between weeks 11 and 14 of gestation, of which 44 per cent were performed prior to week 14. The mean culture time was 14.5 days. Karyotyping was successful in 99.7 per cent of cases. In 9.9 per cent of cases, there was pseudomosaicism with a high rate of loss of an X-chromosome and structural aberration of chromosome 1, which may be due to the Chang medium. The mosaic rate was 0.5 per cent. The overall aberration rate was 2.8 per cent. Our data confirm the reliability of early amniocentesis, which is a serious alternative to standard amniocentesis and chorionic villus sampling (CVS).